A penetration process into granular materials is common and of great interest both in nature (e.g. root growth) and in engineering (e.g. the cone penetration test common in civil engineering or core sampling methods for investigating submarine geology). The Discrete Element Method (DEM), which is a powerful tool for investigating interactions between granular materials and tools, e.g. mixing [1], can be used to study such a penetration process. However, comparisons between numerical and physical experiments are needed to validate and facilitate the interpretation of simulations. Due to their opaque and granular nature, it is generally difficult to assess the stress and deformation states induced by a penetration process. Recently, Tei et al. successfully tracked plant root growth underground using a novel distributed fiber optic sensor system [2]. In this study, a similar distributed fiber optic sensor system is designed to measure the strain induced by the penetration of a needle into glass beads. Accordingly, we performed large-scale DEM simulations for the penetration process into granular packing with equivalent particle size and average density. Since the fundamental information from the DEM simulations is particle-wise, but the measured data from the sensors are naturally homogenized from the surrounding particles, we investigated several homogenized quantities to find the one that best fits the experimental data.

References

[1]    Chen, J., Kitamura, K., Barbieri, E., Nishiura, D. and Furuichi, M. (2022) Analyzing effects of microscopic material parameters on macroscopic mechanical responses in underwater mixing using discrete element method, Powder Technology, 401, 117304.

[2]    Tei, M., Barbieri, E., Soma, F., Uga, Y. and Kawahito, Y. (2022) Agritech imaging of underground plant root growth using a distributed fiber optic sensor. In Optical Fibers and Sensors for Medical Diagnostics, Treatment and Environmental Applications XXII )